MXPA99006818A

MXPA99006818A - Polyme dispersions

Info

Publication number: MXPA99006818A
Application number: MXPA/A/1999/006818A
Authority: MX
Inventors: Robert David Solomon; Gary David Greenblatt
Original assignee: Rohm And Haas Company
Priority date: 1998-07-24
Filing date: 1999-07-22
Publication date: 2000-04-24

Abstract

The present invention relates to: Aqueous dispersions of copolymers formed by the emulsion polymerization of a monomer mixture including certain terminally unsaturated oligomers, which are capable of demonstrating low viscosities over a wide range of

Description

POLYMER DISPERSIONS This invention relates to polymer dispersions. More particularly, the present invention relates to dispersions of polymers that are capable of demonstrating low viscosities over a wide pH range. It is known that aqueous dispersions of carboxylic acid containing polymers have many applications, including their use as binders in coating compositions. In general, these polymer dispersions are formed from the emulsion polymerization of a mixture of ethylenically more saturated monomers containing up to 20% by weight of a carboxylic acid containing monomer, such as acrylic acid (AA) or acid methacrylic (MAA). These polymer dispersions demonstrate relatively low viscosities at low pH levels, for example, pH 3-5, but tend to demonstrate significantly higher viscosities at higher pH levels, for example, 8 to 10. Polymer dispersions can be formulated with low viscosities to include higher polymer solids, for example, 50% by weight of polymer solids, while in comparison, dispersions with high viscosities can be formulated only to include minor polymer solids, eg, 40% by weight solids of polymer. Accordingly, in order to reduce transport costs, the manufacturer of Polymers would prefer to supply customers with dispersions of high polymer solids, with low pH. Since coating compositions, such as paints, are generally formulated at a pH in the range of 8 to 10, and as the polymer manufacturer likes to provide the coating manufacturer with an easy-to-use dispersion, dispersion of the polymer is preferably supplied at an appropriate high pH. However, the formulation of polymer dispersions of high solids in paints at a high pH may result in coagulation or gel formation of the formulation. Accordingly, the carboxylic acid containing the polymer dispersions that are traditionally supplied at the high pH has either a relatively lower solids content and / or includes a significant amount of anionic surfactant. This means that not only the transport costs of the polymer manufacturer are higher, since it has to transport relatively more water in the dispersion, but also the coating compositions have to contain relatively higher amounts of water and / or surfactant. These problems are particularly acute when it is desired to manufacture dispersions of polymers of high solids, where the particle size of the polymer is required to be very small, for example, 100 nm or less. These dispersions tend to be highly viscous at high pHs, and consequently, they require very high levels of anionic surfactants to allow their manufacture even in relatively low polymer solids. A process for the preparation of dispersions of fine particle plastics from a monomer mixture consisting of several ethylenically unsaturated monomers, including from 0.1% to 5% by weight of an acid , unsaturated monocarboxylic, is presented in US-A-4193902.

The process involves metering the monomer mixture simultaneously with an initiator into an aqueous liquor containing 0.5 to 10% by weight of an anionic emulsifier, polymerizing the monomers to form the dispersion, and adjusting the dispersion to a pH of 7. to 10. The quantitative ratio of the monomers to the water is selected such that the resulting dispersion contains from 20 to only 45% solids. Dispersions of polymers formed from a monomer mixture including from 8 to 20% by weight of a C, -C5 mono- or C4-Ce dicarboxylic acid or anhydride are presented in US-A-5356968. The dispersions, which may include from 10 to 60% by weight of solids, are obtained by the emulsion polymerization of the monomers in the presence of a mixture of the emulsifier which includes at least two anionic emulsifiers and optionally one or more nonionic emulsifiers. The mixture is present in a amount from 0.5 to 7% by weight based on the weight of the monomers. The average particle size of the polymer in the dispersion is from 60 to 100 nm. Although it has been reported that to produce only a small increase in viscosity at about pH 7-10, relatively large amounts of the free radical initiator are required, the increase in viscosity as the pH increases to 7-10. It is still quite significant. US-A-5141814 discloses particles of addition polymers with core shells, stabilized in a non-ionic manner, with an average diameter of 100 nm maximum, where the core includes an addition polymer and is insoluble in water and water. cover includes polyoxyalkylene chains with an average chain length of from 6 to 25 oxyalkylene units per chain. At least 20 percent of the chains are covalently linked to the nucleus and there are enough chains in the nucleus in such a way that the ratio of the core mass to the shell is 98: 2 to 60:40. Although these spatially stabilized dispersions are described as relatively insensitive to changes in pH and the dispersions are exemplified as having a high solids content, only small proportions can be tolerated, for example up to 5% by weight of the core polymer , of ionic monomers such as acrylic acid and methacrylic acid. In addition, manufacturers they have environmental pressures to reduce or eliminate the use of polyoxyalkylenes. In DE-A-4026640, it is explained that the oligomeric carboxylic acids can be used as stabilizers for the emulsion polymerization of unsaturated monomers in an olefinic manner, and that this leads to dispersions of coagulate-free and extremely stable fine-particle polymers in their shell . The dispersions may contain from 20 to 65% by weight of dispersed polymer with an average particle diameter of less than 100 nm. In the worked examples, the stabilizer is present in an amount of from 16 to 46% by weight of polymer. There is no explanation or suggestion that oligomeric carboxylic acids would be useful for stabilizing dispersions of carboxylic-containing polymers. Aqueous coating and lacquer compositions including a copolymer grafted with functional carboxylic acid macromonomers attached at one terminal end thereof to a polymeric backbone are described in WO-A-9532228 and O-A-95322255, respectively. Although the references generally have to do with the polymerized macromonomer from the carboxylic functional monomers, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and its anhydrides, macromonomers based on the methacrylic acid and only macromonomers based on methacrylic acid are exemplified. Dispersions of high solids of copolymers formed from methacrylic acid based macromonomers can be prepared with small particle sizes. However, the worked examples (see for example, Example 8 worked) indicate that the copolymers formed from the macromonomers based on methacrylic acid are not able to demonstrate low viscosities at a high pH, such as, for example, a pH 9. An object of the present invention is to provide the dispersion of a carboxylic acid-containing polymer, which is capable of demonstrating low viscosities over a wide pH range. A further objective of this invention is that the dispersion can be manufactured by conventional emulsion polymerization techniques and does not essentially require the use of significant amounts of the anionic surfactant. According to the present invention, an aqueous dispersion of a copolymer formed by the emulsion polymerization of a monomer mixture is provided which includes: a) from 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula: where N is a residue of the formula: CH2 CH- COOH where M is the residue of an ethylenically unsaturated monomer; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; and b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, aromatic vinyl compounds containing compounds including up to 20 carbons, ethylenically unsaturated nitriles containing from 3 to 6 carbons, vinyl halides and non-aromatic hydrocarbons containing from 2 to 8 carbons and at least an olefinic double bond. The term "the mentioned residues N and M are randomly arranged in the aforementioned oligomer" means that the residue adjacent to the unsaturated moiety terminally it can be either a N or M residue, that the residue adjacent to the residue adjacent to the terminally unsaturated half can be either a N or M residue, and so on. Surprisingly, although the aqueous dispersions of the present invention may include a relatively high acid content, they are capable of demonstrating low viscosities over a wide pH range. That a dispersion can demonstrate low viscosities over a wide pH range allows the polymer manufacturer to prepare the dispersion with a high solids content and a high pH. In addition, it allows the polymer manufacturer to prepare the dispersion with a very fine particle size. According to another aspect of the present invention, there is provided a method for the preparation of an emulsion polymer having an average particle diameter no greater than 250 nm, wherein the method includes subjecting a monomer mixture containing: a) 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula: where N is a residue of the formula CH2 CH- COOH where M is the residue of an ethylenically unsaturated monomer; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; and b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, aromatic vinyl compounds containing compounds including up to 20 carbons, ethylenically unsaturated nitriles containing from 3 to 6 carbons, vinyl halides and non-aromatic hydrocarbons containing from 2 to 8 carbons and at least an olefinic double bond; to a free radical polymerization in the presence of 0.5 to 10% by weight of an anionic amulsifier. Preferably, the method includes the additional step of adjusting the aforementioned dispersion to a pH of 7 to 10. The mixture of the monomer that is polymerized to form the dispersion of the polymer of the present invention of preference includes from 1 to 10%, more preferably from 2 to 8% by weight of the terminally unsaturated oligomers mentioned a). Suitable terminally unsaturated oligomers a) are known in the art. Preferably, the terminally unsaturated oligomers mentioned are those defined above but where m is in the range of 0 to 20 and where n is in the range of 3 to 20. More preferably, m is 0 and n is found in the range from 3 to 10. Suitable processes for the manufacture of the oligomers a) are described in US-A-4056559, US-A-5710227, US-A-5587431, US-A-4680352, US-A-4694054 and US Pat. EP-0779305. M is preferably a residue of the formula CH2 CX- R whereX! is -H or -CH3, R is a phenyl radical, a vinyl radical, -CONH2, -CN or -COOX2, X2 is an alkyl radical (C2 to CB), a vinyl radical or an allyl radical. More preferably, M is a residue of one or more ethylenically unsaturated monomers selected from the group consisting of methylacrylate, ethyl acrylate, butyl acrylate, ethylhexyl acrylate, styrene, isoprene, butadiene, vinyl acetate, acrylamide, acrylonitrile, allylmethacrylate. , methyl methacrylate, ethyl methacrylate and butyl methacrylate. The appropriate monomers b) are alkyl (meth) acrylates. { C1 to C4), preferably (C 1 to C 8) alkyl (meth) acrylates, more preferably methyl methacrylate, ethyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate, and glycidyl (meth) acrylates, preferably glycidyl methacrylate. The acrylic and methacrylic acid amides are preferably acrylamide. Vinyl esters of carboxylic acids with from 1 to 20 carbons are preferably vinyl laurate, vinyl stearate, vinyl propionate and vinyl acetate, more preferably vinyl acetate. Aromatic vinyl compounds containing up to 20 carbons are preferably vinyltoluene, styrene, ethylstyrene, butyl styrene and decylstyrene, more preferably styrene. The ethylenically unsaturated nitriles containing from 3 to 6 carbons are preferably acrylonitrile and methacrylonitrile. The vinyl halides are preferably vinyl chloride and vmylidene chloride. The non-aromatic hydrocarbons having 2 to 8 carbons and at least one olefinic double bond are preferably butadiene, isoprene and chloroprene. The monomers b) are preferably selected from the group consisting of methyl (meth) -crylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) decile acrylic, (met) lauryl acrylate, (met) isobornyl acrylate, isodecyl (met) acrylate, (meth) oleyl acrylic acid, (meth) palmityl acrylate, (meth) estenium acrylate, styrene, butadiene, vinyl acetate, vinyl chloride, vmylidene chloride, acrylonitrile, metacplonitplo, acplamide and glycidyl metacrylate. The mixture of the monomer that is polymerized to form the polymer dispersion of the present invention can optionally include up to 10% by weight of other copolymerizable monomers. Other suitable copolymetable monomers are preferably selected from the group consisting of the hydroxyethyl (meth) acutate, hydroxypropyl (meth) acrylate, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, mono-methyl itaconate, fumarate mono-methyl, monobutyl fumarate, maleic anhydride, substituted acplamides, diacetone acplamide, acetoacetoxyethyl methacrylate, acrolein, methacrolein, dicyclopentadienyl metacrate, dimethyl meta-isopropenyl benzyl isocyanate, isocyanate ethyl methacrylate, methyl cellulose, hydroxyethyl cellulose , ethylene, propylene, N-vmilo pyrrolidone and N, N'-dimethylamine (met) acplato. The polymer particles of the dispersion of the present invention preferably have an average diameter of not more than 250 nm, more preferably not greater than 100 nm and still more preferably in the range of 40 to 100 nm. The polymer dispersion of the present invention can be formed through any emulsion polymerization unit technique suitable for the emulsion polymerization of monomer mixtures including up to 20% by weight of the mono- or dicarboxylic acid monomer . These techniques are well known in the art. For example, the emulsion polymerization process described in US-A-5356968 is very suitable for the preparation of the polymer dispersions of the present invention. The emulsion polymerization must be carried out in the presence of an ammonium emulsifier. These emulsifiers are well known in the art and include particularly, although not exclusively, alkali metal salts of sulfuric acid, semi-esters of phenols or alkyl alcohols, which may be ethoxylated, sulphates of ethoxylated alcohols, phosphoric acid esters, alkyl and aplo sulfosuccmates, and alkyl or aryl sulfonates . The molecular weights of the emulsion polymers of the present invention are preferably not greater than 2 million, more preferably not greater than 1 million, in accordance with what is measured by gel penetration chromatography. Although the process of the present invention can be used to prepare the emulsion polymers having molecular weights greater than 1 million, it is particularly suitable for the preparation of the emulsion polymers to have molecular weights of 1 million or less. The aqueous dispersions according to the present invention can be used in the preparation of aqueous dispersions with a multimodal particle size distribution, for example, bi-modal. Accordingly, in a further aspect of the present invention, there is provided an aqueous dispersion of polymer particles with a multimodal distribution of the particle size, and including at least one copolymer formed by the emulsion polymerization of a mixture of the monomer including: a) from 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula: (I) COOH where N is a residue of the formula CH2 CX- I COOH where Xx is selected from the group consisting of H and CH3; where is the residue of an unsaturated monomer so ethylenic; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, aromatic vinyl compounds containing compounds including up to 20 carbons, ethylenically unsaturated nitriles containing from 3 to 6 carbons, vinyl halides and non-aromatic hydrocarbons containing from 2 to 8 carbons and at least an olefinic double bond; and c) from 0 to 10% by weight of other copolymerizable monomers. Preferably at least one mode of the multimodal particle size distribution has an average particle diameter of from 40 to 100 nm. More preferably, a significant portion of at least one mode, having an average particle diameter of from 40 to 100 nm, includes the at least one copolymer mentioned.

The preparation and use of bimodal emulsion polymers are well known in the art, for example in accordance with that disclosed in US-A-4539361 and US-A-5624992. Particularly, the present invention can be useful for making stable emulsion polymers containing particles with a four to ten fold difference in particle size in high solids without limitations in pH or viscosity. The polymer dispersions of the present invention can be used in or as compositions for different applications including, without limitation, coatings such as paints, primers and varnishes, binders for nonwovens and textiles, dispersants such as pigment dispersants, paper coatings, coatings skin, adhesives, floor polishers, caulks and elastomeric wall mastics. The dispersions can be used on their own or in combination with one or more dispersions of polymers. The invention will be described more specifically at this time in terms of the following examples of some preferred embodiments that are provided for purposes of illustration only, and can be compared with the comparative tests also provided below. EXAMPLES Preparation of terminally unsaturated oligomers Oligomers A, B and C were prepared substantially in accordance with the procedures described in US-A-5710227. The oligomers are not neutralized. Oligomer A was prepared with 29% solids in water with Mw = 1199 and Mn = 485. The oligomer B was prepared with 30% solids in water, subsequently the water was reduced in vacuo producing material in 66% solids, with Mw = 336 and Mn = 204. The oligomer C was prepared with 27% solids, with Mw = 595 and Mn = 390. Comparative Example N \ 1 (5% MAA) One polymer per emulsion was prepared in a conventional manner (substantially in accordance with the procedure described in US-A-5356968). A mixture of monomers was prepared by combining 210 g of deionized water, 7.7 g of ammonium salt of lauryl sulfate, 408 g of methyl meta-plate, 255 g of 2-ethylhexyl-platelet, 18 g of styrene, and 36 g of methacrylic acid. The monomer mixture was emulsified by performing the mixture under standard conditions. 350 g of deionized water and 58 g of the ammonium salt of lauryl sulfate were charged to a three-liter flask, and the contents heated to 83-85 ° C. 40 g of the emulsified monomer mixture was charged to the flask, followed by 9.8 g of an 18% aqueous solution of ammonium persulfate. After an exotherm of four degrees, the mixture of the emulsified monomer and 58 g of a 0.6% aqueous solution of ammonium persulfate solution were added from linearly and separately for 150 minutes while maintaining the temperature of the contents at 83-85 ° C. After completing the additions, the contents of the flask were cooled to 65 ° C. The remaining monomer was reduced by the sequential addition of aqueous ferrous sulfate, aqueous tertiary butyl hydroperoxide and sodium sulfoxylate formaldehyde. The neutralized polymer was added at a pH of 7.4 with ammonia and the Kathon brand LX biocide. The product was diluted with deionized water to provide a polymer solids level of 42.4% by weight. The latex had an average particle diameter of 60 nm and a viscosity of 1000 cps (centipoise). Comparative Examples N] 2 and 3 Comparative Examples Ni 2 and 3 were prepared in substantially the same manner as Comparative Example Ni 1. Comparative Examples Ni 2 and 3 differed in composition, acid and solid level: Comparative Ni 2 (8 % MAA) The ratio of the emulsified monomer mixture was 200 g of deionized water, 7.7 g of ammonium salt of lauryl sulfate, 394 g of methyl methacrylate, 248 g of 2-et? L-hexylaclate, 18 g of styrene, and 58 g of methacrylic acid, and 4 g of n-dodecyl mercaptan. The initial reactor charge was 691 deionized water, 58 g ammonium sulfate salt of lauplo. The final latex was 37.6% by weight of solids, with an average particle diameter of 48 nm, pH = 6.4, and a viscosity of 768 cps. Comparative Ni 3 (8% MAA) The ratio of the emulsified monomer mixture was 200 g of deionized water, 7.7 g of ammonium salt of lauryl sulfate, 394 g of methyl methacrylate, 248 g of 2-ethyl-hexylacrylate , 18 g of styrene, and 58 g of methacrylic acid, and 4 g of n-dodecyl mercaptan. The initial reactor charge was 350 deionized water, 58 g of ammonium salt of lauryl sulfate. The final latex was 43.9% by weight of solids, with an average particle diameter of 61 nm, pH = 6.7, and a viscosity of 1444 cps. Example Ni 4 (5% Oligomer A) This emulsion polymer was prepared substantially in accordance with that described in Comparative Example 1, in a conventional manner. A monomer mixture was prepared by combining 223 g of deionized water, 9.5 g of ammonium sulfate salt of lauplo, 509 g of methyl methacrylate, 304 g of 2-ethylhexyl acrylate, 22 g of styrene, and 152 g of a 29% aqueous solution of Oligomer A. The monomer mixture was emulsified by mixing under standard conditions. 510 g of deionized water and 71 g of ammonium salt of lauryl sulfate were charged to a three-liter flask, and the contents heated to 83-85 ° C. 40 g of the emulsified monomer mixture was charged to a flask, followed by 12.2 g of a 18% aqueous solution of ammonium persulfate. After a four-stage exotherm, the mixture of the emulsified monomer and 45 g of a 1.0% aqueous solution of ammonium persulfate solution were added in a linear and separate manner for 150 minutes while maintaining the temperature of the content of the mixture. -85 ° C. After completing the additions, the contents of the flask were cooled to 65 ° C. The remaining monomer was reduced by the sequential addition of aqueous ferrous sulphate, aqueous tertiary butyl hydroperoxide and sodium sulfoxylate formaldehyde. The neutralized polymer was added to a pH of 4.2 with ammonia and the Kathon brand LX biocide. The product was diluted with deionized water to provide a polymer solids level of 44.0% by weight. The dispersion of the polymer had an average particle diameter of 62 nm and a viscosity of 41 cps. Examples Nj 5 to 8 Examples Ni 5 to 8 were prepared in substantially the same manner as Example Ni 4 but differed in composition, Oligomer level, and solids. Example Ni 5 (5% Oligomer A, highest solids) The ratio of the monomers used was 421 g of methyl meta-plate, 392 g of 2-et? L-hex? Lacrylate, 22 g of styrene, and 152 g of a 29% aqueous solution of Oligomer A. The emulsified monomer mixture and 45 g of a solution 1.0% aqueous ammonium persulfate solution was added linearly and separately to 360 g of deionized water, 71 g of ammonium salt of lauryl sulfate. The final latex was 48.9% by weight of polymer solids, with an average particle diameter of 83 nm, pH = 3.7, and a viscosity of 308 cps. Example Ni 6 (5% Oligomer B) The ratio of the monomers used was 509 g of methyl meta-plate, 304 g of 2-ethylhexyl acrylate, 22 g of styrene, and 66 g of a 66% aqueous solution of the Oligomer B. The monomer mixture and 45 g of a 1.0% aqueous solution of ammonium persulfate solution were added linearly and separately to 510 g of deionized water, 71 g of ammonium salt of lauryl sulfate. The final latex was 43.5% by weight of polymer solids, with an average particle diameter of 62 nm, pH = 3.8, and a viscosity of 29 cps. Example Ni 7 (2% Oligomer A) The ratio of the monomers used was 430 g of methyl methacrylate, 409 g of 2-ethylhexyl acrylate, 22 g of styrene, and 61 g of a 29% aqueous solution of the Oligomer A. The monomer mixture and 45 g of a 1.0% aqueous solution of ammonium persulfate solution were added linearly and separately to 525 g of deionized water, 56 g of ammonium salt of lauryl sulfate. The final latex was 44. 7% by weight of polymer solids, with an average particle diameter of 86 nm, pH = 5.8, and a viscosity of 55 cps. Example Ni 8 (8% Oligomer A) The ratio of the monomers used was 408 g of methyl methacrylate, 379 g of 2-ethylhexyl acrylate, 22 g of styrene, and 243 g of a 29% aqueous solution of the Oligomer A. The monomer mixture and 45 g of a 1.0% aqueous solution of ammonium persulfate solution were added linearly and separately to 510 g of deionized water, 56 g of ammonium salt of lauryl sulfate. The final latex was 44.8% by weight of polymer solids, with an average particle diameter of 93 nm, pH = 4.5, and a viscosity of 26 cps. Comparative Example Ni 9 (5% MAA) This emulsion polymer was prepared in a conventional manner (substantially in accordance with that described in US-A-5356968). A monomer mixture was prepared by combining 255 g of deionized water, 7.4 g of sodium salt of lauryl sulfate, 441 g of methyl methacrylate, 374 g of butyl acrylate, and 43.4 g of methacrylic acid. The monomer mixture was emulsified by mixing under standard conditions. 600 g of deionized water and 113.5 g of the sodium salt of lauryl sulfate were charged to a three liter flask, and the contents heated to 83-85 ° C. 91 g of a 4.7% aqueous solution of ammonium persulfate to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. After completing the additions, the contents of the flask were cooled to 65 ° C. The remaining monomer was reduced by the sequential addition of aqueous ferrous sulfate, aqueous tertiary butyl hydroperoxide and sodium sulfoxylate formaldehyde. The neutralized polymer was added at a pH of 6.2 with ammonia and the Kathon brand LX biocide. The product was diluted with deionized water to provide a polymer solids level of 44.6% by weight. The emulsion had an average particle diameter of 57 nm and a viscosity of 67 cps. Comparative Example Ni 10 Comparative Example Ni 10 was prepared in substantially the same manner as Comparative Example Ni 9. Comparative Example Ni 10 differed at the level of acid, soap and solids: Comparative Example Ni 10 (2% MAA) A mixture of monomers was prepared by combining 405 g of deionized water, 2.8 g of dodecylbenzene sulfate, 5.5 g of polyethoxy nonylphenol sodium salt, 472 g of methyl methacrylate, 401 g of butyl acrylate, and 18.4 g of methacrylic acid. 462 g of deionized water, 37.2 g of dodecylbenzene sulfate, 111 g of sodium salt of polyethoxy- nonylphenol and 113.5 g of sodium sulfate salt of 1 to a three-liter flask, and the contents were heated to 83-85 ° C. 13 g of a 22% aqueous solution of ammonium persulfate was added to the reactor. The mixture of the emulsified monomer and 45 g of a 1.6% aqueous solution of ammonium persulfate was added in a linear manner and separately for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The product was diluted with deionized water to provide a polymer solids level of 44.9% by weight. The latex had an average particle diameter of 76 nm at a pH of 6.3 and a viscosity of 90 cps. Example Ni 11 (5% Oligomer A) This emulsion polymer was prepared in substantially the same manner as described above in Comparative Example Ni 10. A mixture of monomers was prepared by combining 240 g of deionized water, 6.1 g of sodium salt of lauryl sulfate, 461 g of methyl metaplatter, 393 g of butyl acrylate, and 60.6 g of a 29% solution of Oligomer A. The monomer mixture was emulsified by mixing under standard conditions. 600 g of deionized water and 93.4 g of the sodium salt of lauplo sulfate were charged to a three-liter flask, and the contents were heated to 83-85 ° C. 92 g of a 4.7% aqueous solution of ammonium persulfate was added to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. After completing the additions, the contents of the flask were cooled to 65 ° C. The remaining monomer was reduced by the sequential addition of aqueous ferrous sulfate, aqueous tertiary butyl hydroperoxide and sodium sulfoxylate formaldehyde. The neutralized polymer was added at a pH of 4.0 with ammonia and the Kathon brand LX biocide. The product was diluted with deionized water to provide a polymer solids level of 44.6% by weight. The latex had an average particle diameter of 68 nm and a viscosity of 227 cps. Examples Ni 12 to 16 Examples Ni 12 to 16 were prepared in substantially the same manner as Example Ni 11. Examples Ni 12 to 16 differed in the Oligomer, Oligomer level, composition and solids: Example Ni 12 (2% Oligomer B) The ratio of the monomers used was 445 g of methyl methacrylate, 378 g of butyl acrylate and 25.4 g of a 66% aqueous solution of Oligomer B. 665 g of deionized water and 111 g of the salt were charged of sodium lauryl sulfate to a three-liter flask, and the contents were heated to 83-85 ° C. 89 g of a 4.7% aqueous solution of ammonium persulfate was added to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The final latex was 44.2% by weight of polymer solids, with an average particle diameter of 51 nm, pH = 4.1, and a viscosity of 182 cps. Example Ni 13 (5% Oligomer B) The ratio of the monomers used was 303 g of methyl methacrylate, 257 g of butyl acrylate and 44.6 g of a 66% aqueous solution of Oligomer B. 460 g of water were charged deionized and 78 g of the sodium salt of lauryl sulfate to a three-liter flask, and the contents were heated to 83-85 ° C. 63 g of a 4.7% aqueous solution of ammonium persulfate was added to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The final latex was 44.2% by weight of polymer solids, with an average particle diameter of 53 nm, pH = 2.8, and a viscosity of 50 cps. Example Ni 14 (5% Oligomer C) The ratio of the monomers used was 303 g of methyl methacrylate, 257 g of butyl acrylate and 111 g of a 27% aqueous solution of Oligomer C. 425 g of water were charged deionized and 78 g of the sodium salt of lauryl sulfate to a three-liter flask, and the contents were heated to 83-85 ° C. 63 g of a 4.7% aqueous solution of ammonium persulfate was added to the reactor. The monomer mixture emulsified was added linearly for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The final latex was 43.7% by weight of polymer solids, with an average particle diameter of 54 nm, pH = 2.6, and a viscosity of 324 cps. Example Ni 15 (5% Oligomer A) The ratio of the monomers used was 303 g of methyl methacrylate, 257 g of butyl acrylate and 104 g of a 28% aqueous solution of Oligomer A. 585 g of water were charged deionized and 63 g of the sodium salt of lauryl sulfate to a three-liter flask, and the contents were heated to 83-85 ° C. 63 g of a 4.7% aqueous solution of ammonium persulfate was added to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The final latex was 39.3% by weight of polymer solids, with an average particle diameter of 45 nm, pH = 2.4, and a viscosity of 114 cps. Example Ni 16 (5% Oligomer A, higher solids) The ratio of the monomers used was 303 g of methyl methacrylate, 257 g of butyl acrylate and 104 g of a 28% aqueous solution of Oligomer A. 280 g of deionized water and 63 g of the sodium salt of lauryl sulfate to a three-liter flask, and the contents were heated to 83-85 ° C. 63 g of a 4.7% aqueous solution was added of ammonium persulfate to the reactor. The emulsified monomer mixture was added in a linear fashion for 120 minutes while maintaining the temperature of the content at 83-85 ° C. The final latex was 49.7% by weight of polymer solids, with an average particle diameter of 77 nm, pH = 2.1, and a viscosity of 3920 cps. Mixture of Ultrafine Latex and Large Particle Size Latex Example Ni 17: (Large mode for mixing study) This emulsion polymer was prepared substantially in accordance with that described in US-A-5356968. A monomer mixture was prepared by combining 338 g of deionized water, 27 g of dodecylbenzene sulfonate, 2082 g of butyl acrylate, 161 g of acrylonitrile, and 58 g of acrylic acid. The monomer mixture was emulsified by mixing under standard conditions. 854 g of deionized water was charged to a three liter flask, and the contents heated to 84-86 ° C. 41 g of a polymer per emulsion was charged to a flask, followed by 20.4 g of a 27% aqueous solution of sodium persulfate. The emulsified monomer mixture and 98 g of a 4.1% aqueous solution of sodium persulfate solution were added linearly and separately for 180 minutes while maintaining the temperature of the content at 84-86 ° C. After completing the additions, the contents of the flask were cooled to 65 ° C. The remaining monomer is reduced by the sequential addition of aqueous ferrous sulfate, ethylenediammatetraacetic acid, aqueous tertiary butyl hydroperoxide and isoascorbic acid. The polymer was neutralized to a pH of 5.7 with sodium hydroxide. The product was diluted with deionized water to provide a polymer solids level of 58.1% by weight. The emulsion had an average particle diameter of 400 nm and a viscosity of 349 cps. Example Ni 18: (mixture of 90/10 Large mode / Ultra-fine mode) 11g of Example Ni 14 were neutralized to a pH of 5.2 with ammonia. The viscosity of this ultrafine emulsion was 18 cps. This latex was added by stirring in 99 g of Example 17. The mixture was 56.7% solid polymer, pH = 5.55 and the viscosity was 57 cps. The mixture is left to stand at room temperature for 24 hours. After 24 hours, there were no signs of sedimentation, the pH was 5.54 and the viscosity was 54 cps. Example Ni 19: (mixture of 75/25 Large mode / Ultra-fine mode) 27.5 g of Example Ni 14 were neutralized to a pH of 5.2 with ammonia. The viscosity of this ultrathin latex was 18 cps. This latex was added by stirring in 82.5 g of Example 17. The mixture was 54.5% solid polymer, pH = 5.57 and the viscosity was 38 cps. The mixture is left to stand at room temperature for 24 hours. After 24 hours, there were no signs of sedimentation, the pH was 5.55 and the viscosity was 36 cps. Stability Tests Each of the previous latexes was tested for stability, first over a range of pHs and subsequently for a period of time at 60 ° C at a pH of 8. 1. The pH viscosity profiles were determined measuring the viscosity of 150 g of each polymer by emulsion at a pH of 3, 7 and 9 in a Brookfield viscometer, model DV-I, at 25 ° C using an appropriate spindle and speed. The initial pH of each polymer per emulsion was adjusted to 3.0 with 5% hydrochloric acid or 28% ammonium hydroxide, and the viscosity was measured. Each example was subsequently adjusted to a pH of 7 and a pH of 9 with 28% ammonium hydroxide and the viscosity was measured. 2. The viscosities of the thermal stage at a high pH were determined by adjusting the pH of samples of 150 g of the polymer per emulsion to a pH of almost 9 without coagulating the sample. The viscosity was measured in a Brookfield viscometer, model DV-I, at 25 ° C using an appropriate spindle and speed. The samples were stored in a 60 ° C oven. The viscosities were remeasured after 1, 2 and 4 weeks at 60 ° C. The results of the tests are shown in Table A below: Table A Latex Viscosity pH Profile (cps at 25 ° C) Viscosity Profile Thermal Stage (cps at 60 ° C) Viscosity Viscosity Viscosity pH Viscosity Viscosity Viscosity Viscosity pH = 3 pH = 7 pH = 9 Time O 1 week 2 weeks 4 weeks 1 NM 1000 4220 8 4220 Gelified 2 NM 700 30000 8 30000 3 NM 3648 gelled 8 Gelled 4 40 35 29 9 29 165 258 172 5 243 390 346 9 346 457 623 747 6 25 43 38 9 38 23 28 29 6 41 50 71 9 71 80 93 154 8 36 40 58 9 58 69 65 78 9 NM 248 > 10000 8 1890 Gelled 10 NM 100 1508 8 1508 7640 8690 19000 11 4700 133 2598 9 155 190 190 264 12 3120 37 30 9 35 30 66 69 13 52 80 31 9 31 33 43 65 14 82 30 33 9 33 32 31 35 15 52 90 74 9 74 39 44 50 16 3080 340 608 9 2320 2592 3284 3508 1. PH profiles - Viscosity There are four key observations: First, the comparative examples show a very large dependence on the pH in the viscosity. Compare them Examples 1, 2 and 3, where the latexes are either gelatinized or irreversibly swollen. As the acid level increases, the increase in viscosity is greater. This shows the limitation of using a conventional acid to stabilize a latex. This invention is particularly demonstrated when we compare example number 3 (8% MAA stabilizer) with example number 8 (8% oligomeric stabilizer). Second, the experimental examples of the invention have viscosities that are pH independent. Compare examples 4-8 and 13-15. The viscosities are low, but more significantly, the viscosities are substantially constant over the pH range. This effect is demonstrated at the low and high levels of the oligomeric stabilizer. Third, although the viscosities of the dispersions of the invention are proportional to the solids, the impact of the solids is reduced, see examples number 15 and 16. The same oligomer was loaded at identical levels. The example of higher solids has the highest viscosity. However, the difference in viscosity is small considering that there is a difference of 10% in solids.

Fourth, some of the experimental examples of the present invention have viscosities that actually decrease when the pH is increased, see examples 11 and 12. 2. Data on the Thermal Stage Viscosity The thermal stage stability test demonstrates the stability of the viscosity at an elevated temperature. This test is an accelerated indicator of shelf life. The comparative examples should not be tested at a pH of 9 due to the instability of their inherent environmental temperature at a high pH. Comparative examples 1, 2, 3, 9 and 10 could only be tested at a pH of 8. Even at a pH of 8, after the thermal stage, the comparative samples were coagulated or irreversibly thickened to unacceptable levels. The experimental examples of the present invention were tested at a pH of 9. All were fairly stable during the course of the experiment. Very low viscosities at a high pH were maintained under the stressing conditions of the test. Although the examples of high solids number 5 and 16 had viscosities that increased by a factor of two, the final viscosities were still relatively low. After the thermal stage tests were completed, all experimental examples of the present invention could be used for subsequent tests.

Claims

CLAIMS 1. An aqueous dispersion of a copolymer formed by the emulsion polymerization of a monomer mixture including: a) from 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula: COOH where N is a residue of the formula: - CH2 CH ~ COOH where M is the residue of an ethylenically unsaturated monomer; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, vimlo aromatic compounds containing compounds including up to 20 carbons, ethylenically more unsaturated nitpho containing from 3 to 6 carbons, vinyl halides and non-aromatic hydrocarbons containing from 2 to 8 carbons and at least one olefinic double bond; and c) from 0 to 10% by weight of other copolymetable monomers.
2. An aqueous dispersion according to that determined in claim 1, wherein said dispersion has a solids content of the polymer in the range of 40 to 70% by weight.
3. An aqueous dispersion as set forth in claim 1, wherein the monomer mixture includes up to 10% by weight of other copolymectable monomers c) selected from the group consisting of: (met) hydroxyethyl acrylate, (meth) actable of hydroxypropyl, acrylic acid, methacrylic acid, crotonic acid, fumápco acid, maleic acid, mono-methyl itaconate, mono-methyl fumarate, monobutyl fumarate, maleic anhydride, substituted acplamides, diacetone acrylamide, acetoacetoxyethyl methacrylate, acrolein, methacrolein, dicyclopentadienyl metacrate, dimethyl meta-isopropenyl benzyl isocyanate, isocyanate ethyl metacrate, methyl cellulose, hydroxyethyl cellulose, ethylene, propylene, N-vmyl pyrrolidone and N, N "I dimethylamine (meth) actable.
4. An aqueous dispersion according to that determined in claim 1, wherein the polymer particles of the dispersion of the present invention have an average diameter no greater than 250 nm.
An aqueous dispersion according to that determined in claim 5, wherein the polymer particles of the dispersion of the present invention have an average diameter of no greater than 40 to 100 nm.
6. A method for the preparation of an emulsion polymer having an average particle diameter of no greater than 250 nm, wherein this method includes subjecting a monomer mixture including: a) from 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula: where N is a residue of the formula: CH2 CH- I COOH where M is the residue of an ethylenically unsaturated monomer; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, villic esters of carboxylic acids containing from 1 to 20 carbons, aromatic compounds of vmilo containing compounds including up to 20 carbons, nicotins ethylenically saturated containing 3 to 6 carbons, vmilo halides and non-aromatic hydrocarbons containing 2 to 8 carbons and at least an olefinic double bond; and c) from 0 to 10% by weight of other copolymetable monomers; to a polymerization of free radical in the presence of 0.2 to 10% by weight of an ammonium emulsifier.
7. A method according to that determined in claim 6, wherein the percentage by weight of the solids of the polymer in the dispersion is 40-70%.
8. An aqueous dispersion of polymer particles with a multimodal distribution of the particle size, and including at least one copolymer formed by the emulsion polymerization of a monomer mixture including • a) from 0.1 to 20% by weight of one or more more saturated oligomers terminally of the formula: where N is a residue of the formula: - CH2 CH- I COOH where X? it is selected from the group consisting of H and CH,; where M is the residue of an ethylenically unsaturated monomer; where the mentioned residues N and M are randomly arranged in the aforementioned oligomer; where m is the total number of residues M in the aforementioned oligomer and is in the range of 0 to 47; where is the total number of residues N in the oligomer mentioned and is in the range of 2 to 140; and where the sum of n and m is in the range of 3 to 150; b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohols containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, aromatic vinyl compounds containing compounds including up to 20 carbons, ethylenically unsaturated nitriles containing from 3 to 6 carbons, vinyl halides and non-aromatic hydrocarbons containing from 2 to 8 carbons and at least one olefinic double bond; and c) from 0 to 10% by weight of other copolymerizable monomers.
9. An aqueous dispersion according to that determined in claim 8, wherein at least one mode of the multimodal particle size distribution has an average particle diameter of from 40 to 100 nm.
10. An aqueous dispersion as set forth in claim 9, wherein an important portion of at least one mode, having an average particle diameter of from 40 to 100 nm, includes the at least one copolymer mentioned.